If you allow other administrators, coordinators, blog authors, etc. to add custom tags when they add items to your website, you may end up with multiple tag synonyms (for example, having both "bike" and "bicycle" as separate tags), misspelled tags or even duplicates. You can merge tags together to clean up your tag list.
Find the tag you want to merge into another tag and click the Merge icon. Choose the tag you want to merge into; if you want to merge into another custom tag, select All Tags as your filter.
When you're ready, click Save. All old tags will be automatically replaced by the tag it was merged with.